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Building Tips and technical articles. => Building techniques => Topic started by: Motorman on December 20, 2013, 06:36:07 PM

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Post by: Motorman on December 20, 2013, 06:36:07 PM: blank
Title: Re: Sub 600 Wing (Electric)
Post by: jim gilmore on December 20, 2013, 10:01:07 PM: I'm confused by this question....
form follows needs....
why cut the wing at all ?
If your talking full fuse why not fit it over the wing or under the wing?
Title: Re: Sub 600 Wing (Electric)
Post by: RC Storick on December 21, 2013, 11:02:44 AM: Quote from: Motorman on December 21, 2013, 09:38:15 AM
I want to keep the vertical CG and the thrust line pretty much on center. Don't really know how important that is but, I've got a Flight Streak with the battery hanging fully below the wing and it flys like a goose with a broken wing.

MM

Its important that's why my MC72 splits tether line with the battery. BATTERY IS KING! Of coarse it only me with no engineering degree just practical experience.
Title: Re: Sub 600 Wing (Electric)
Post by: Serge_Krauss on December 21, 2013, 11:55:23 AM: If you put the bellcrank behind the spar, the leadouts might bend enough to increase wear and friction past what you'd like - but maybe not. Perhaps though you could put the battery between the main spar and leading-edge spar (if you have one), and place the bellcrank inboard of the battery. Maybe you could counter the weight of the bellcrank by offsetting the battery slightly and re-route/bend the control rod to suit? I share your structural concern, although I've seen some wings survive OK, even when notched out past what seems structurally sound to me. 'just some thoughts.

SK
Title: Re: Sub 600 Wing (Electric)
Post by: Kevin Ferguson on December 21, 2013, 02:42:25 PM: Put half the cells above the wing, half below.
Title: Re: Sub 600 Wing (Electric)
Post by: 55chevr on December 21, 2013, 03:09:05 PM: The ARF Flite Streaks we mount the battery on about a 30* angle. The rear of the battery is above the leading edge (actually resting on it) and front of the battery is below the wing center line . The weight is centered on the vertical CG.
Title: Re: Sub 600 Wing (Electric)
Post by: Howard Rush on December 21, 2013, 04:40:03 PM: I have the same problem, though for a different reason. I'm making a take-apart wing that is attached at three points to the fuselage side: top and bottom of the spar and the TE. Most of the lift comes from the front quarter of the wing, so I was worried about getting that load to the spar and not having the LE deflect up or down, which would make the plane fly crummy. I asked a pro airplane stress man, who said just to reinforce the dickens out of the spars: three plies of .007" unidirectional carbon on the forward, aft, and inside faces of each 1/4"-square balsa spar cap halfway out the wing. He didn't seem concerned about the LE deflection. I'll have the LE surrounded by fillet attached to the fuselage, so it won't go anywhere. If you don't have a take-apart airplane, I'd take care of the LE deflection problem by also gluing the front of the wing to the fuselage side. I did that in my current plane, which has a battery bay that goes back into the wing beyond the LE. I used a lighter battery and farther forward CG than I originally intended, so I now use that space for other electrickery.

Update 12/23: The stress man in question came to the house yesterday. I was complaining about his excessive conservatism in specifying all that carbon in the spar. He said that by three plies of carbon, he meant one (1) on each of the three faces of each spar. I have a really, really strong spar now, although it's a little heavy. I'm not going to start over.
Title: Re: Sub 600 Wing (Electric)
Post by: Howard Rush on December 23, 2013, 11:50:29 AM: The bellcrank is a little behind the spar. It's aways behind the CG.
Title: Re: Sub 600 Wing (Electric)
Post by: RC Storick on December 23, 2013, 08:50:15 PM: Quote from: Howard Rush on December 23, 2013, 11:50:29 AM
The bellcrank is a little behind the spar. It's aways behind the CG.

As per prior threads it just don't matter, Or does it?? LL~
Title: Re: Sub 600 Wing (Electric)
Post by: Serge_Krauss on December 23, 2013, 10:16:02 PM: 'usually kinda hard to put it anywhere else...
Title: Re: Sub 600 Wing (Electric)
Post by: RC Storick on December 23, 2013, 10:36:46 PM: Quote from: Serge_Krauss on December 23, 2013, 10:16:02 PM
'usually kinda hard to put it anywhere else...

Start watching this video at 1.08 and listen to Windy

http://www.youtube.com/watch?v=3gL-xnUYiMU
Title: Re: Sub 600 Wing (Electric)
Post by: Howard Rush on December 24, 2013, 12:55:11 AM: I listened. He is wrong.
Title: Re: Sub 600 Wing (Electric)
Post by: RC Storick on December 24, 2013, 06:03:48 AM: Quote from: Howard Rush on December 24, 2013, 12:55:11 AM
I listened. He is wrong.

Well your at least starting to catch on by moving the battery. LL~ LL~
Title: Re: Sub 600 Wing (Electric)
Post by: Dennis Adamisin on December 24, 2013, 07:51:49 AM: Choose your pack carefully: For a 550 sq airplane plan on a 4Sx2500, There are two main form-factor packs around that size.

* The "brick" packs are around 35mmm by 35mm x 105mm. Shorter packs mean that the weight of the back can be located farther aft (or forward if needed). I have not had to notch an LE any more than 1" using short packs This shape of pack also enables you to look at a vertical pack (see Sparky's MC72) if you can make the fuse a little tall up front. Plan B: use cheek cowls and run the pack ACROSS the fuse...

* The "Wafer" packs are around 28mm x 44mm x 135mm. These packs have the advantage of lowest shift in vertical CG. If you mount the bellcrank in a normal location you might box out the arm and let the notch for the pack go only 1/3 to 1/2 the depth of the airfoil and back to the spar. Still have to pay attention to the CG but there less pain. I recently took this approach. on a short nosed 1948 design.

* One approach I have not tried but that I believe would work is to use one of the thin packs but locate it in the WING 1 bay outboard of the bellcrank. Center of the pack would be roughly 2" off center, if the pack weighs 9 oz then that is 18 n-oz or the same as a 3/4 oz slug of tip weight located 24" off the center - HEY the airplane just got 3/4 oz lighter! Off course you have to work out details of carry through strucure (easy) and a LE cap battery hatch but shat should be no big deal... Battery effect on CG will be pretty close to nothing, you will have to fine tune the CG the old fashioned way.
Title: Re: Sub 600 Wing (Electric)
Post by: RC Storick on December 24, 2013, 10:03:00 AM: As Windy stated and I believe Bill said also as long as its mounted behind the CG. Bellcranks mounted on boards don't have centrifugal force imposed on them. Gravity is not the same. I try to plot a design so that everything is in line. It makes for a plane where no weight is added to balance things.

Instead of hanging boards a test bed need to be built where we can shift the weight and bellcrank locations easily. This is the ONLY way I and many others will be convinced of this. Paper equations don't fly. Instead of moving weight around move point of tether (which most believe is the wing tip) (but forget the leverage imposed by the distance from center of belcrank to leadout guide) Let alone the centrifugal force added. But I am sure there are some pie times radius square formals that can be written down. But until you feel it in the handle mean ZIP.

So I say mount you bellcrank anywhere you feel it belongs and exit the wing where ever you think is best. Makes me no mind. I have given up in trying to reason.

Not directed at anyone person.

Just as I did with my battery mount standing straight up in front of the wing (I will let you know the results of this experiment soon) Test flights may take place Friday. In order to do this the tail must be light because it still has to balance. Having built only 4 electric airplanes it didn't take me long to see the obstacles that need to be over come. They are only getting better in feel as I move the battery back. No its not a cg shift. Take weight out not add to balance.

If I were going to do something goofy in belcrank mounting it would be to mount the bell crank on the outboard tip so that the leverage imposed by the lines running the length of the wing may overcome some of the yaw. But inline is most pratical.
Title: Re: Sub 600 Wing (Electric)
Post by: RC Storick on December 24, 2013, 01:38:09 PM: Quote from: Dennis Adamisin on December 24, 2013, 07:51:49 AM
Choose your pack carefully: For a 550 sq airplane plan on a 4Sx2500, There are two main form-factor packs around that size.

* The "brick" packs are around 35mmm by 35mm x 105mm. Shorter packs mean that the weight of the back can be located farther aft (or forward if needed). I have not had to notch an LE any more than 1" using short packs This shape of pack also enables you to look at a vertical pack (see Sparky's MC72) if you can make the fuse a little tall up front. Plan B: use cheek cowls and run the pack ACROSS the fuse...

(http://stunthanger.com/smf/index.php?action=dlattach;topic=33653.0;attach=138773;image)
Title: Re: Sub 600 Wing (Electric)
Post by: Doug Moon on December 24, 2013, 02:05:22 PM: I listened to what he said and he stated that if the BC is ahead of the CG you are always pulling the plane towards you and the LOs make no difference. Then he said if you place it anywhere behind the CG its ok. I was really kind of shocked to hear him say the LOs make no difference. I have flown one of his planes in Nats trim and it is quite obvious he knew the importance of LO position.

If you are in fact pulling the plane in at you in one aspect, BC ahead if the CG, than how can you NOT be doing the same thing in the other aspect, BC after the CG? If you are pulling the nose in on forward mount you would be pulling the tail in on a rearward mount. That is not a logical conclusion. AND I AM NO ENGINEER either but I can tell you what he said is not logical.

At a glance it would appear with the BC ahead of the CG that the nose would be pulled in. BUT, you cant discount the fact that there is a rudder on there helping to create the ACTUAL direction of flight. The LOs position is then used to get the model as close to tangent to the circle.

I am no engineer, math wizard (hell, I barely got out of high school geomtry, and my grammar sucks too), rocket scientist, statistician, excel guru, or whatever the name of the day happens to be. But I can tell you after years of learning the art/Voodoo of trimming and really understanding the relationship between the LO position, TW, and CG position, along with a host of other little items that truly effect the model it doesn't take a rocket scientist, or any of the other scientist types, to figure out that the BC position is just about the least of ones worries when it comes to getting a model to fly straight, true, with repeatable results in just about any weather condition....... That is the goal correct? At least that it is mine.
Title: Re: Sub 600 Wing (Electric)
Post by: Doug Moon on December 24, 2013, 02:07:05 PM: Robert,

Did you move the BC aft on the new plane to accomodate for the new aft CG placement by moving the battery weight more reward?

Where does it balance?
Title: Re: Sub 600 Wing (Electric)
Post by: RC Storick on December 24, 2013, 02:16:53 PM: This is not a engineering thing. Its logic. Draw it out on paper with the point of tether ahead of the CG. Point of tether is not the wing tip its the bellcrank pivot. Tether meant attached to. It is not attached to the wing tip. There is a mechanical advantage between the leadout guide and the bellcrank pivot. As long as this is behind the CG (according to Wild Bill) all is well. Put it ahead one time and see how it feels. No good! Kind of a double standard he states that is as long as its behind the CG in one sentence and it the next it don't matter. Oh well.

Now on your drawing move it back farther and look at the relationship between the CG and pivot. The longer axis will make it feel more nose heavy and it will also load the nose (or at least it feels that way)

I am done trying to make people understand this and you wont until you make a plane is this configuration (I have). So mount then anywhere you feel is best and put leadouts anywhere you think is best.
Title: Re: Sub 600 Wing (Electric)
Post by: RC Storick on December 24, 2013, 02:18:57 PM: Quote from: Doug Moon on December 24, 2013, 02:07:05 PM
Robert,
Did you move the BC aft on the new plane to accomodate for the new aft CG placement by moving the battery weight more reward?

There is no aft CG its in the same place. MAKE THE TAIL Lighter. Keep pivot, lead outs and tip weight in a straight line close to CG as you can. You just need to know when to stop painting.

CG is determined by cord and airfoil ,not by length of plane. Maybe a math genius will chime in and prove me wrong but that's how I have always done it. Final CG adjustment is done in test flights. My Gort eyeball engineering has yet to let me down.

Quote from: Doug Moon on December 24, 2013, 02:07:05 PM
Where does it balance?

Root cord it 9.75 and it balances 2.125 back from LE so whatever percentage that is it looks close. The new airplane was designed around the premise to move the concentrated weight back so the tail had to be adjusted in length and weight. Instead of making things longer or adding clay to balance make things shorter and lighter to balance. If it's lighter you don't need as much leverage to move the object. Starting and stopping quicker with less clock time. Its all a experiment and I will let you know one way or the other but I think I am onto something with this electric stuff.
Title: Re: Sub 600 Wing (Electric)
Post by: Doug Moon on December 24, 2013, 02:32:10 PM: Quote from: Robert Storick on December 24, 2013, 02:16:53 PM
This is not a engineering thing. Its logic. Draw it out on paper with the point of tether ahead of the CG. Point of tether is not the wing tip its the bellcrank pivot. Tether meant attached to. It is not attached to the wing tip. There is a mechanical advantage between the leadout guide and the bellcrank pivot. As long as this is behind the CG (according to Wild Bill) all is well. Put it ahead one time and see how it feels. No good! Kind of a double standard he states that is as long as its behind the CG in one sentence and it the next it don't matter. Oh well.

Just so you know, I have never read the famous Wild Bill article you and others keep referring to. My logic is found on the circle at the bottom of a fuel can and guess what? It doesnt support what you have been saying. But if it does for you then more power to you.
Title: Re: Sub 600 Wing (Electric)
Post by: RC Storick on December 24, 2013, 02:36:46 PM: Congrats Doug
Title: Re: Sub 600 Wing (Electric)
Post by: 55chevr on December 25, 2013, 11:07:37 AM: Not sure why you have to put the battery aft of the spar. I have 5 electric ships and all balance well without getting into the spar. On the ARF Flight Streak the battery is angle above the leading edge but still way forward of the spar.

Joe
Title: Re: Sub 600 Wing (Electric)
Post by: Howard Rush on December 25, 2013, 07:16:14 PM: If the airplane has a really long nose or short tail or a heavy motor, you might locate the battery aft to make the CG come out right. For a stunt plane, that probably wouldn't be the best way to get the CG to come out right.
Title: Re: Sub 600 Wing (Electric)
Post by: George Grossardt on January 03, 2014, 06:52:29 PM: Very interesting thread. I have been trying to decide if I should build the original Stiletto, which I believe is about 590 square inches, with electric power. I haven't measured to see if a battery will fit without cutting into the leading edge of the wing yet. Has anyone done this on the original Stiletto? Any concerns I should be thinking about other than the leading edge issue?

George
Title: Re: Sub 600 Wing (Electric)
Post by: Avaiojet on January 04, 2014, 09:45:54 AM: My understanding has always been for a given airframe, with lifting airfoils placed somwhere in the design, wing and stab, you find the CG using both MAC's.

Once you have the CG for that design, how can you make it different? It is what it is.

Robert's idea of moving mass towards the CG isn't new by any standards. And placing all the on board stuff to maintain that already known CG, for that particular design, should be quite typical.

Now, if I'm missing something here, please, just let me know.

I design for looks. ;D

In most cases, I can find CG's for my designs. n~

I'm designing and will be building that model with an extreamly long nose moment and short tail moment.

Obviously, from some viewpoints, and stunt math, this should be the reverse.

So be it because I like the design.

Charles

P.S. My bellcranks are always on the CG. And I have no idea why. LL~ LL~ LL~
Title: Re: Sub 600 Wing (Electric)
Post by: Crist Rigotti on January 06, 2014, 10:59:22 AM: Quote from: Motorman on December 20, 2013, 06:36:07 PM
I've come to realize the smaller planes need the battery farther back. On a full fuselage with a 550 sq. in. wing I think I need to cut the center section out of the wing all the way back to the spar.

So how do you get that strength back? What size/type of wood do I need in the spar?

Would there be any problems at the lead out guide putting the bellcrank behind the spar?

Thanks,
MM

Where, in percentage of MAC, do you plan to locate the CG?